1. Field of the Disclosure
The present disclosure relates to a quantum dot thin film solar cell.
2. Description of Related Art
Solar cell is a very promising clean energy, which can directly produce electricity from sunlight. If a quantum dot effect is applied to the solar cell, an energy conversion rate thereof can be greatly improved. The so-called quantum dot effect generally relates to the following two effects.
One effect is an impact ionization (II) effect. In semiconductor material, when energy of two bandgaps is provided from external, excited electrons may exist in form of hot electrons. When the hot electrons are transited form high energy level to low energy level excitation state, the released energy can excite another electron from a valence band to a conduction band, and such phenomenon is referred to as the impact ionization effect. According to such effect, one high-energy photon can excite two or a plurality of hot electrons.
Another effect is an Auger recombination (AR) effect relative to the impact ionization effect, which refers to that in the semiconductor material, the energy released due to recombination of hot electron and hole can excite another hot electron to transit to a higher energy level, so as to prolong a lifetime of the hot electron in the conduction band.
When the semiconductor material displays a quantum dot size, the continuous conduction band is gradually split into small energy levels, so that a cooling speed of the electrons is slowed down, and therefore the impact ionization effect and the Auger recombination effect can be effectively utilized. According to theoretical calculations, the traditional single junction solar cell only can achieve 31% energy conversion efficiency, and if combining with the ionization and Auger recombination effects, the maximum theoretical efficiency of the solar cell can be 66%, which definitely shows a potential of using the quantum dots in the solar cell.
In a present dye-sensitized solar cell (DSSC), nano quantum dots are added into the solar cell. However, an energy conversion rate of the solar cell is low due to a poor interface adhesion between nano-crystals and an optical active layer, which is even worse than a situation without adding the quantum dots.
Although U.S. Patent Publication No. 20080230120 and Taiwan Patent Publication No. 200810136 all provide a nano photovoltaic device with quantum efficiency, a nano-crystal layer thereof is independent, so that regarding a whole structure thereof, a transparent conductive film or a tunnel junction is added, which may increase a fabrication cost.